Silver halide photothermographic imaging materials, often referred to as `dry silver` compositions because no liquid development is necessary to produce the final image, have been known in the art for many years. These imaging materials basically comprise a light-insensitive, reducible silver source, a light-sensitive mateial which generates silver when irradiated, and a reducing agent for silver ion in the silver source. The light-sensitive material is generally photographic silver halide which must be in catalytic proximity to the light-insensitive silver source. Catalytic proximity is an intimate physical association of these two materials which enables catalysis of the reduction of the silver source by silver specks formed on the silver halide. Exposure of the silver halide to light produces small clusters of silver atoms. The imagewise distribution of these clusters is known in the art as the latent image. This latent image generally is not visible by ordinary means and the light-sensitive article must be further processed in order to produce a visual image. The visual image is produced by the catalytic reduction of silver ions which, as already noted, are in catalytic proximity to the specks of the latent image.
The silver source used in this area of technology is a material which contains a reducible source of silver ions. The earliest and still preferred source comprises silver salts of long chain carboxylic acids, usually of from 10 to 30 carbon atoms. The silver salt of behenic acid or mixtures of acids of like molecular weight have been primarily used. Salts of other organic acids or other organic materials such as silver imidazolates have been proposed, and U.S. Pat. No. 4,260,677 discloses the use of complexes of inorganic or organic silver salts as image source materials.
Color-forming, `dry silver` imaging systems are known in the photographic art. Color-formation is based on the oxidation/reduction reaction between the light-exposed silver salt of a fatty acid which has been halidized and dye-sensitized to a specific wavelength and is used with a chromogenic developer in the presence of elevated temperature. For example, U.S. Pat. No. 3,531,286 teaches the inclusion of color coupler components such as a p-phenylenediamine developer and a phenolic or active methylene coupler in close proximity to the light-sensitive emulsion, J. W. Carpenter and P. W. Lauf, Research Disclosure No. 17029, issued June 1978, review prior art relating to photothermographic silver halide systems which include color formation.
U.S. Pat. No. 4,021,240 discloses the use of sulfonamidophenol reducing agents and four equivalent photographic color couplers in thermographic and photothermographic emulsions to produce dye images including multicolor images.
U.S. Pat. No. 3,985,565 discloses the use of a certain class of phenolic type photographic color couplers in photothermographic emulsions to provide a color image.
U.S. Pat. No. 3,531,286 discloses the use of photographic phenolic or active methylene color couplers in photothermographic emulsions containing p-phenylenediamine developing agents to produce dye images.
Research disclosure 177006, published January 1979, discloses a photothermographic material containing an azo dye reducing compound, 2,2',6,6'-tetrachlorobiphenol as an auxiliary developing agent, in combination with a development modifier such as N-hydroxynaphthalimide.
U.S. Pat. No. 4,021,250 discloses thermally developable photosensitive material comprising certain dihydroxybiphenyls as reducing agent in the presence of certain polyarylamino compounds. No color-forming properties are recognized.
G.B. Pat. No. 2,075,496 discloses a wet process for producing black and white or color photographic images. Certain bisphenols are stated to be useful as dye-forming developing agents.